Doctor blade for coating apparatus



Feb. 21, 1967 E. WARNER DOCTOR BLADE FOR COATING APPARATUS,

Filed Feb. 20, 1963 INVENTOR. EDGAR WARNER ATTORNEYS United StatesPatent Oflice 3,304,910 Patented Feb. 21, 1967 3,304,910 DOCTOR BLADEFOR COATING APPARATUS Edgar Warner, Middletown, Ohio, assignor toChampion Papers Inc., Hamilton, Ohio, a corporation of Ohio Filed Feb.20, 1963, Ser. No. 259,943 6 Claims. (Cl. 118-104) The presentapplication is a continuation-in-part of my co-pending applicationSerial No. 52,348 filed August 29, 1960, now United States LettersPatent No. 3,084,663 issued on April 9, 1963 for a Doctor Blade forCoating Apparatus.

The present invention relates to a method of and apparatus for themanufacture of a coated web and coated sheet material. One aspect of theinvention resides in providing a method and apparatus for forming acoating on a moving web or sheet. Another aspect of this inventionresides in a method and apparatus for forming a coating on a travellingweb by means of a magnetically positioned coating means. While theinvention has applicability to a wide variety of coating procedures andproducts and materials to be coated, it is particularly advantageous inapplying a coating composition containing mineral pigment and adhesiveto a travelling paper web and will be described in conjunction with thecoating of such a Web by Way of illustration and not as a limitation.

The manufacture of coated paper by a doctoring process of the naturehere involved is generally represented in United States Patents Nos.2,598,733 and 2,729,192 both issued to Edgar Warner on June 3, 1952 andJanuary 3, 1956, respectively. The coating procedure usually comprisesthe application of an excess of an aqueous dispersion of a mineralpigment and an adhesive to the surface of a moving web and subsequentremoval of the surplus over and above the amount of coating compositionrequired to form a coating of the desired dry Weight on (of coating) thesurface of the web. In such a process the paper web absorbs aqueousvehicle from the portion of the applied coating layer in contacttherewith to form a filter cake, which is firm enough to resist thewiping action of the doctor which then rides on the surface of thefilter cake and wipes off the overlying fluid coating composition.

My co-pending application represents an improvement in doctor devices.in that it permits the application of greater coating weights per unitarea by means of a moving doctor surface there illustrated as includinga revolvable cylindrical rod having circumferential alternately arrangedribs and grooves. The rod is therein received in a partial socketextending along the rod and having spaced apart terminal edges wherebythe rod is enabled to engage the workpiece, e.g. a travelling paper webhaving an excess of aqueous coating to be removed.

The present invention is an improvement on United States Patent No.2,774,329 issued to Smith on December 18, 1956. The Smith patent isentirely incorporated herein by reference and teaches a doctoring devicehaving a revolvable doctor rod of magnetic material magnetically held inposition by magnetic or electromagnetic means (hereinafter collectivelycalled magnetic means). The present invention includes a magnetic meansto position a revolvable cylindrical rod having circumferentialalternate ribs and grooves.

One object of the present invention is to provide a self-cleaning doctorrod and a method of coating paper employing the same.

One object of the present invention is to provide in a magnetic holderan improved doctor rod and a cleaning means therefor.

. in side elevation,

A specific object of the present invention resides in providing a methodand apparatus for forming on a moving cellulosic web a coating with amagnetically positioned cylindrical moving doctor surface havingalternately arranged peripheral ribs and grooves A further and broaderobject of the invention resides in providing a method and apparatus forforming coating with a magnetically positioned doctor rod Still anotherobject resides in providing a method of and apparatus for the formationof a coating on paper, paperboard, and like surfaces with a magneticallypositioned doctor rod.

The apparatus of the present invention may be described as constitutingan improvement in the combination of a revolvable cylindrical doctor rodand a magnetic holder means for maintaining the rod in position duringthe forming of a coating on a web. One aspect of the improvementcomprises a doctor surface on the doctor rod that is composed of aseries of alternately arranged circumferential ribs and grooves. Anotheraspect of the improvement also includes a means for cleaning the doctorsurface.

One embodiment of the aforesaid improvement includes a means forcleaning which is a member extending generally parallel to the doctorrod and which is complementarily shaped to engage the ribs and groovesof the doctor surface. I

Briefly, a method according to the invention is for forming a coating ona moving web with a magnetically moving doctor rod and includes theimprovement of moving the web with an excess of coating thereon past amoving plurality of alternately arranged ribs and grooves which extendslaterally of the web and cleaning the ribs and grooves with acomplementarily shaped member. In the course of this method the step ofmoving causes removal of excess coating from the web.

One embodiment of the method includes cleaning the ribs and grooves froma position underneath the doctor rod. Another aspect of the methodincludes cleaning the ribs and grooves from one side of the doctor rod.

A further aspect of the invention resides in the manner in which thecomplementarily shaped cleaning member is formed. One aspect of thisinvolves employing an elongated strip with a sharpened edge which isthen held against the moving doctor rod and is thereby worn in to theproper conforming shape. This causes the shape of the strip or cleaningmember to conform to the profile of the doctor rod.

One feature of the invention is an enhanced self-cleaning arrangement. Amajor feature of the invention is an improvement in the weight ofcoating which is applied in one pass through a coater mechanism. Stillanother major feature of the invention is the applicability of. a doctorrod with alternating circumferential ribs and grooves combined with amagnetic positioning means.

Other objects, advantages, and features will become apparent from thefollowing more detailed description read in conjunction with thedrawings wherein:

FIG. 1 is a view of a doctor blade, as viewed from above FIG. 2, withthe web removed, according to the present invention, showingschematically the components presently involved.

FIG. 2 is a side view through section 22 of FIG. 1 showing oneembodiment of the apparatus along the normally horizontal axis of thedoctor rod according to the present invention.

FIG. 2A is a partly cutaway schematic elevation as seen from the left ofthe FIG. 2 embodiment, for example as applied to the system of FIG. 5.

FIG. 3 is another embodiment, shown schematically applicable to thesystems of FIGS. 1

and wherein the doctor rod is cleaned from one side, and as viewed along22 of FIG. 1.

FIG. 4 is an enlarged portion of FIG. 3 schematically representing oneembodiment of a cleaning strip arrangement.

FIG. 5 is a diagram schematically illustrating the manner in which theinvention may be incorporated into a coating procedure.

Where appropriate, the same reference numerals are employed throughoutthe specification. For the purpose of clarifying the fact that thepresent invention is applicable to a variety of coating systems, thedisclosures of the aforesaid Warner patents and my copending applicationNo. 52,438 are incorporated herein by reference.

Referring now in particular to FIGS. 1 and 2, it will be seen that thedoctor blade comprises the doctor rod and a magnetic holder therefor.The doctor rod 10 is formed from a steel rod which has been machined,rolled or otherwise worked by one or the other of several methods toprovide a doctor surface defined by a series of concentric alternatelyinterdigitated circumferential ribs 2 and grooves 4 of ostensiblythreadlike profile configuration. It is most significant to note thatthese ribs and grooves are defined as thread-like. They do not comprisea thread in that there is no spiral progression of the valley as is thecase of a thread wherein the groove between adjacent ribs would becontinuous throughout the length of the article provided with the threadfrom one end to the other. Rather in the present invention each groovebetween any two adjacent ribs is an annular recess extending around thecircumference of the rod and singularly each circumferential groove iscompletely independent one from the other. As has been stated theprofile configuration of the hills and valleys 2 and 4 may bethread-like in profile appearance. A standard Whitworth profile is oneembodiment. Of course the thread profile may assume a variety ofconfigurations, for example, the Whitworth profile itself may bemodified such that the tops of the ribs and the bottoms of the groovesmay be slightly rounded rather than as angulated as shown in thedrawing. Thus in general, it may be said that the thread-like profile,if Whitworth, of these alternating ribs and grooves should be such thatthe included angle between any two adjacent surfaces defining a valleyshould approximate 90.

The doctor rod is made from magnetic material such as a steel rod. Therod is chromium plated by any suitable process after the describedprofile has been imparted to its surface. The depth from top of the ribs2 to the floor of the valleys 4 may be varied.

As the profile depth may be varied so also may the number of ribs perinch length of rod be varied. In my co-pending application, for example,the range of from 50 to 150 ribs or threads per inch along the entirelength of the doctor rod 10 has been employed though this dimension mayalso vary.

Referring to FIGS. 2 and 2A, it is seen that the magnetic holder 20 maycomprise a pair of magnetic members 21, 22 extending vertically intocontact with a horizontally arranged doctor rod 10. The doctor rod issupported in a seat 23 formed at the ends of the members 21 and 22. Themagnetic holder 20 may comprise either a permanent magnet or anelectromagnet. The members 21 and 22 are conveniently constructed asshown for the pole-pieces in the said Smith patent. The holder 20 may bemounted in the embodiments of FIGS. 1 and 5 hereof as shown in FIG. 4 ofthe said Smith patent.

An alternate arrangement is to provide members 21 and 22 as magnetsindependent of each other with element 21 having its south pole adjacentthe rod 10 and element 22 having its north pole adjacent to rod 10. Thepolarities may be reversed.

Referring again to FIG. 2 and FIG. 2A, the cleaning means 25 is shown asclamped at a position intermediate the two poles of the magnetic holder.The means 25 is of resilient nonmagnetic material, i.e. stainless steeland is provided for cleaning the doctor surface from underneath the rodand preferably comprises a member complementarily shaped to engage theribs and grooves on the doctor surface. It is supported by a clampcomprising clamping bar 26 and a plurality of clamping bolts 27threadedly engaged therewith. The bar 26 and bolts 27 are of nonmagneticresilient nonabsorbent material. The complementarily shaped edge 28 ofthe strip 25 has ribs 28a and grooves 28b thereon which areinterdigitated with the ribs and grooves 2, 4 on the rod 10 so that theribs on 28 extend into the grooves 4 on the rod 10 and the ribs 2 on therod extend into the grooves on the strip 28.

It will be observed from the embodiment of FIGS. 2 and 2A that thecleaning means is supported at a position intermediate the poles of themagnets so as to clean the doctor rod from underneath. The groove 23formed at the ends of the magnetic support members 21, 22 is elongatedand extends in parallelism with the axis of the doctor rod. Moreover aplurality of passages 29 are provided through at least one leg of themagnetic holder 20, illustrated as the leg 21. The upper end of theclamping bar 26 is cut off to be approximately even with the bottom ofthe hole 29, whereby a passage 30 is formed from underneath the rod downpast the cleaning means 25 and out through the ports 29. This passageprovides a drain for excess coating removed from a traveling web, andwould be applicable for example in the embodiment of FIG. 5.

In FIGS. 3 and 4 there is illustrated an embodiment for cleaning thedoctor rod 10 from one side of the magnet. In this embodiment a cleaningstrip 40 is mounted by a clamping bar 41 and a plurality of clampingbolts 42 so that one edge thereof is engageable with the doctor rod 10.The member 40 is preferably of a soft but resilient material. It isadvantageously formed by (FIG. 4) originally forming a sharp edge 44 onone end of the strip and rolling or otherwise bending such edge over sothat it can be held against the revolving doctor. Initially the sharpedge rides on the crest of the ribs 2. After a period of running the rodwith the sharp edge against it, the edge 44 wears so that the dottedline position of FIG. 4 is assumed wherein the ends of the rod extenddown into the grooves and the ribs 2 of the rod ride in the wornportion. Returning to FIG. 3, the magnetic holder 20 is constructed inone of the fashions suitable for FIG. 1 and a nonmagnetic plug 45 isinserted between the two legs 21, 22. The excess material therefore willbe removed from the rod 10 and flow down over the cleaning strip 40 aswell as the clamping mechanism 41, 42. The clamping mechanism andcleaning means (elements 40, 41, 42) are of nonmagnetic material, e.g.stainless steel.

On occasion it may be desirable to offset the bias caused by theresilient action of cleaning strip 40 against the doctor 10. In suchcase an additional cleaning strip may be mounted opposite the member 40to contact the opposite side of the doctor 10. An alternative embodimentis to put a soft magnetic facing 46 on the opposite face of the magnet(here shown as the upper end of leg 22) whereby the resiliency of member40 will cause a wearing in of the member 46 against the rod. Cleaningstrip 40 may be of stainless steel.

The circumferential grooves 4 operate as a series of metering devicesarranged laterally of the web to permit coating to pass between theindividual chambers formed by grooves 4 and the web as the lattercontacts the tops of the ribs 2.

Referring to FIGS. 1, 2, 3 and 5, the rod 10 is driven or rotated,preferably counterclockwise (on occasion, clockwise) as shown, in holder20 preferably at an extremely low rate of speed, on the order of from /3feet per minute surface speed. This enhances the self-doctoring featureof the device on a continuous basis and additionally distributes wearevenly throughout the length of the rod 10. The driving mechanism may beconventional, such as an electric motor M coupled to the end of the rodthrough a speed reduction device. In FIG. 1 a drive mechanism isillustrated schematically as comprising a large sprocket 14 driven fromsmall sprocket 8 via chain or belt 12; the large sprocket being mountedon the end of rod the smaller sprocket being carried on shaft 6 drivenby a conventional motor M. A speed reducer, if needed, may be disposedbetween the motor and the sprocket 8. If desired the same shaft 6 couldbe connected to the opposite end of rod 10 such that the rod 10 isdriven from both ends simultaneously. This arrangement is desirable toprevent torsional stresses from being developed in the rod 10 where thedevice is utilized in coating wide webs, such as in the paper makingart.

FIG. 5 illustrates one of many ways of utilizing the invention.Exemplary other techniques for employing the invention are found in mycopending application as well as the above said Warner patents. In FIG.5, a tension blade coater is illustrated wherein the web W passes over arotating applicator roll 50 which carries coating from the pan 51 ontothe web, the coating being smoothed and metered to the correct weight asthe web thereafter passes over rod 10. The tension on the web providesthe requisite action to urge it against rod 10. The rod is constructedas described above. The method according to the invention will be seento include the forming of a coating on a moving web using a magneticallypositioned doctor rod 10. The steps of the method further include movingthe web with an excess of coating thereon (e.g., as applied by the roll50) through a sufficient distance to permit the forming of a filter cakeprior to engaging the doctor rod 10. Then when the web engages thedoctor rod, it will simultaneously engage a plurality of alternatelyarranged ribs and grooves advantageously extending laterally of the weband defining a metering doctor surface on the doctor rod. In thisfashion the excess of coating is removed while at the same timepermitting the application of a greater amount of coating and theformation of a heavier filter cake.

The doctor surface is, in both the method and the apparatus according tothe invention, cleaned by engagement of the ribs and grooves thereofwith a complementarily shaped member. In one embodiment, the cleaning isaccomplished from a position intermediate the magnetic rod supportmembers, from underneath the rod (for example see FIG. 2) and in anotherembodiment the cleaning is accomplished from at least one side (e.g.,FIG. 3). The said members (25, 40) may be of a soft resilientnonmagnetic material selected from the class consisting of metals andresins, for example stainless steel and polytetrafluoroethylene,respectively, and should be nonabsorbent of the fluids and materials inthe coating. Nonabsorbency avoids building up abrasive particles in thecleaning means 25, 40 thereby reducing wear on the rod 10.

The invention further includes forming the contour of the cleaning meansby wearing the same against the doctor surface to the extent that thecleaning means is complementarily shaped to have a serrated edge suchthat the ribs 2 extend into the serrations on the cleaning means and theserrrations on the edge 28 also extend into the grooves 4 on the doctorrod.

While the invention has been described with respect to paper, and paperis referred to in some if not all of claims that follow below, it is tobe understood that this term does not restrict itself to paper as oftenemployed in the conventional sense. The term paper as employed hererefers to webs or sheets formed of natural fiber, synthetic fiber, or acombination of the two whether they are bleached, dyed or the like. Thisterm is used 6 in the application here to refer generically to paper,paperboard, cellulosic webs of all types formed of the materialsindicated above in this paragraph. The single word is used as a matterof convenience and not of limitation.

Paper made in accordance with the present invention may therefore have acoating suitable for printing. As stated in my co-pending application,coating procedures of the general class here involved, and that includesthe present invention, are useful in the production of coated paper andpaperboard for printing purposes.

It will be appreciated that the various serrated cleaning means 25, 40are at least coextensive with the working width of the rod 10, that is,the cleaning means is Wide enough to clean the length of the rodengaging the Web W' for removing excess coating. Also, the resilientaction of the member 40 is preferably maintained by a slight outwardspacing from the pole piece 21 and may have slots whereby it can beslipped into position over bolts 42 as during a replacement operation.The magnetic assembly 20 does not have to have means at its right andleft hand ends (as viewed in FIG. 2A) to close off the passage 30 andmay :be open to provide additional drainage ports in which case aconduit or catch basin ought to be provided to receive any end drainage.

It will be appreciated if the foregoing description and illustratedembodiments are for illustrative and representative purposes only andare not intended as limitations on the scope and spirit of theinvention. The invention is intended to include all those modificationsobvious to one skilled in the art, including the substitution ofequivalents as fall both within the spirit, scope, or terms of the-fOllOWing claims.

I claim:

1. In the combination of a revolvable cylindrical doctor rod and amagnetic holder means having magnetic members for maintaining said rodin position during the forming of a coating on a web, the improvementcomprising a doctor surface on said rod composed of a series ofalternately arranged annular ribs and grooves;

said magnetic members having a seat in contact with said doctor surfaceand supporting said rod; and

a means for cleaning said doctor surface.

2. In combination of claim 1, a means for cleaning that comprises amember of resilient nonmagnetic material nonabsorbent of materials andfluids in the coating and complementarily shaped to engage said ribs andgrooves supported in engagement with said ribs and grooves.

3. The combination of claim 1 wherein the seat of said magnetic holdermeans includes the poles of a magnet shaped to form an elongated groovein which said rod is seated, wherein said means for cleaning comprises aresilient nonmagnetic n'onabsorbent member complementarily shaped toengage said ribs and grooves; and further including means for supportingsaid means for cleaning on one side of both poles of such magnet.

4. The combination of claim 1 wherein said magnetic holder meansincludes the poles of a magnet shaped to form an elongated groove inwhich said rod is supported, wherein said means for cleaning comprises amember complementarily shaped to engage said ribs and grooves; andfurther including in the combination means for supporting said means forcleaning at a position intermediate the poles of such magnet, andconduit means for providing a passage through at least one pole of saidmagnet.

5. The combination of claim 1 where said means for cleaning comprises astrip supported parallel to the axis of said rod with one edge of suchstrip in engagement with and conforming to the profile of the peripheryof said rod.

6. The combination of claim 1 wherein said means for cleaning comprisesa strip supported parallel to the axis of said rod with one edge of suchstrip having a sharp edge in engagement with the periphery of said rodwhereby contact with the doctor surface on said rod wears said edge to aserrated shape in conformance with the doctor surface profile.

References Cited by the Examiner UNITED STATES PATENTS 2,221,441 11/1940Charters 118-118 8 Sherman et a1 118-118 Erther 118118 Smith 118-118Uhleen 118102 X Warner 15256.52 X

RALPH S. KENDELL, Primary Examiner.

ALFRED L. LEAVITT, Examiner.

10 E. B. LIPSCOMB, Assistant Examiner.

1. IN THE COMBINATION OF A REVOLVABLE CYLINDRICAL DOCTOR ROD AND AMAGNETIC HOLDER MEANS HAVING MAGNETIC MEMBERS FOR MAINTAINING SAID RODIN POSITION DURING THE FORMING OF A COATING ON A WEB, THE IMPROVEMENTCOMPRISING A DOCTOR SURFACE ON SAID ROD COMPOSED OF A SERIES OFALTERNATELY ARRANGED ANNULAR RIBS AND GROOVES;